Downhole Apparatus and Method

ABSTRACT

A downhole apparatus ( 10 ) for use in activating a downhole tool (T). The apparatus ( 10 ) comprises a seat ( 18 ) configured to receive an object, such as a ball ( 16 ). The seat ( 18 ) comprises a convex object engaging surface ( 24 ) for engaging the object.

FIELD OF THE INVENTION

This invention relates to a downhole apparatus and method. More particularly, but not exclusively, embodiments of this invention relate to a seat for receiving an object, such as a ball.

BACKGROUND TO THE INVENTION

In the oil and gas exploration and production industry, well boreholes are drilled in order to access subsurface hydrocarbon-bearing formations. A tubular string, such as a completion string or running string, may be made up and run into the borehole and operated to perform a number of different operations in the borehole. Some operations to be carried out may require that one or more tools be activated from a run-in configuration to an activated configuration.

A variety of activation mechanisms may be used. One or more tool may be mechanically activated, for example by applying a force from surface or by running a mechanical activation or setting tool into the bore and applying a force to the tool using the setting tool. Alternatively or additionally, one or more tool may be fluid pressure activated, for example by applying a fluid pressure from surface and/or by hydrostatic pressure. One fluid pressure activation mechanism involves the provision of a reduced inner diameter portion or seat configured to receive a ball. In use, the ball may be run through the tubular string until it lands on the seat. By sealing or restricting the bore of the tubular string, applied fluid pressure may be used to activate a tool, such as a sleeve from a run-in configuration to an activated configuration.

In order to ensure that the ball is safely caught and securely held by the seat, the ball and/or the seat may be configured so as to provide as large an area of contact between the ball and the seat as possible. In some cases, this may be achieved by grinding or otherwise forming either or both of the seat and the ball so that the seat hugs the ball. This also has the effect of reducing stress since forces may be distributed over the larger contact surface area.

While the provision of larger contact surface areas provide a number of benefits, in the high temperature and high pressure environment of some oil and gas well boreholes, conventional arrangements suffer from the drawback that forces between the ball and the seat may be sufficient to cause the ball to become swaged or otherwise lodged in the seat, thereby forming an undesirable permanent obstruction. In some instances, this may result in the tubular string having to be removed from the borehole or additional workover or drilling operations to be carried out to remove or bypass the obstruction, this involving significant time and expense to an operator.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a downhole apparatus or tool comprising:

a seat configured to receive an object, the seat comprising a convex object engaging surface.

The apparatus may comprise a tubular body or housing configured to permit passage of the object.

The object may be of any suitable form and construction. In particular embodiments, the object comprises a ball, in particular but not exclusively, a spherical ball, or the like.

In use, the object may be dropped, pumped or otherwise motivated through the tubular body until it lands on the seat and the apparatus may be utilised in a variety of applications to perform one or more downhole operation or to permit one or more downhole operation to be carried out. For example, the apparatus may be configured so that engagement between the object and the seat may seal or at least restrict fluid passage through the tubular body to increase upstream fluid pressure, the increased upstream fluid pressure being used to perform or permit a borehole operation to be carried out. Alternatively or additionally, the apparatus may be configured so that engagement between the object and the seat may seal or at least restrict fluid passage through the tubular body to provide a fluid pressure differential across the seat, the fluid pressure differential being utilised to perform or permit a borehole operation to be carried out. Alternatively or additionally, the apparatus may be configured so that the impact of the object on the seat may be utilised to perform or permit a borehole operation to be carried out. One or more borehole operation may, for example, comprise moving a downhole tool from a first configuration to a second configuration. The first configuration may comprise a run-in configuration. The second configuration may comprise an activated configuration.

Beneficially, embodiments of the invention may prevent or at least mitigate the swaging, jamming or otherwise lodging of the object in a seat, thereby permitting the obstruction created by engagement of the object with the seat to be removed, for example by fluid pressure or reverse fluid circulation. Embodiments of the invention may alternatively or additionally permit a greater degree of control over the transmission of load forces between the object and the seat, when engaged, and to other components of, or operatively associated with, the apparatus. For example, in embodiments of the invention the engagement between the seat and the object may be configured so that the load path of a resultant force transmitted to the seat may be controlled or selected to increase or maximise the transmission of load forces along a particular vector in order to activate another component of, or operatively associated with, the apparatus and/or to eliminate or mitigate moment forces. Control over the transmission of load forces may additionally or alternatively permit optimisation of parts of the apparatus, or of components operatively associated with the apparatus, since redundancy otherwise required due to the lack of control over the transmission of load forces may be reduced or eliminated.

In particular embodiments, the object engaging surface may comprise, or form part of, an upstream or uphole directed surface of the seat. For example, the apparatus may be configured so that the seat receives an object directed from surface or other upstream or uphole location.

Alternatively or in addition, the object engaging surface may comprise, or form part of, a downstream or downhole directed surface of the seat. For example, the apparatus may be configured so that the seat receives an object directed from a downstream or downhole location.

It will be understood that while the terms uphole, upstream, downhole and downhole are used, the apparatus may be oriented at any required angle or orientation and may be used in a vertical borehole, a deviated borehole or horizontal borehole where required.

The object engaging surface may be of any suitable form and construction.

The object engaging surface may be configured to minimise the contact area between the seat and the object; in contrast to conventional arrangements which seek to maximise the contact area between the seat and the object.

The object engaging surface may be configured to provide a line or point engagement between the seat and the object.

The object engaging surface may comprise a curved convex surface portion. The object engaging surface may comprise a hemi-toroidal surface, d-shaped in longitudinal section or the like.

The object engaging surface may comprise a linear convex surface. For example, the object engaging surface may comprise a toroidal polyhedron surface, triangular in longitudinal section or the like.

In particular embodiments, the object engaging surface may be angled with respect to a longitudinal axis of the body.

The apparatus may be configured to provide a single line or point contact with the object, when engaged. The object engaging surface may be annular.

The apparatus may be configured to provide a plurality of distinct points of contact with the object. For example, the seat may comprise a plurality of circumferentially or radially spaced components or segments.

The apparatus may be configured to provide sealing engagement between the object and the seat. Alternatively, the apparatus may be configured to provide at least partial fluid bypass when the object and the seat are engaged.

The apparatus may be configured to be run into a borehole as part of a tubular string, for example but not exclusively a completion string, running string, drill string or the like. The apparatus may be configured for location at any location in the string. In some embodiments, the apparatus may be configured for location at or near the distalmost end of the tubular string.

The tubular body may be of any suitable form and construction.

The tubular body may comprise a wall and an axial bore. The axial bore may comprise an axial flow passage. The axial bore may be configured to provide a substantially contiguous flow passage with an axial throughbore of the tubular string. In use, the object may be directed through the tubular string from surface or other upstream location and into the axial bore of the tubular body before landing on the seat.

In some embodiments, the tubular body may comprise a lateral fluid flow passage, for example but not exclusively a port. The lateral fluid flow passage may comprise at least one fluid port. The lateral fluid flow passage may comprise a single port. Alternatively, the lateral fluid flow passage may comprise a plurality of ports. In embodiments where a plurality of lateral fluid flow ports, two or more of the ports may be arranged circumferentially. Alternatively, or additionally, two or more of the ports may be arranged axially.

The seat may be of any suitable form and construction.

The seat may comprise a smaller inner diameter than the tubular body.

The seat may be located adjacent/within the tubular body.

The seat may comprise an intermediate portion. The intermediate portion may be disposed or formed between the upstream or uphole directed surface and the downstream or downhole directed surface of the seat.

In some embodiments, the seat may be integrally formed with the tubular body.

In some embodiments, the seat may be coupled to the tubular body.

In some embodiments, the seat may be provided separately from the tubular body and may, for example be provided, coupled to or formed on a bore member, such as a sleeve, operatively associated with the tubular body.

The seat may have a smaller ID than the bore member or sleeve.

The seat may be located adjacent/within the bore member or sleeve.

In use, the tubular body and the bore member or sleeve may together define a downhole tool for performing or permitting a borehole operation to be carried out. The apparatus may be moveable from a first configuration to a second configuration. The first configuration may comprise a run-in configuration. The second configuration may comprise an activated configuration. The bore member or sleeve may be moveable relative to the tubular body to move the apparatus from the first configuration to the second configuration. The apparatus may be configured to prevent lateral passage of fluid through the tubular body when in the first configuration and permit lateral passage of fluid when in the second configuration.

The bore member or sleeve may comprise a lateral fluid flow passage, for example but not exclusively a port. The lateral fluid flow passage may comprise at least one fluid port. The lateral fluid flow passage may comprise a single port. Alternatively, the lateral fluid flow passage may comprise a plurality of ports. In embodiments where a plurality of lateral fluid flow ports, two or more of the ports may be arranged circumferentially. Alternatively, or additionally, two or more of the ports may be arranged axially.

In some embodiments, both the tool and the tubular body may comprise at least one lateral port and the apparatus may be configured to prevent lateral passage of fluid through the tubular body when in the first configuration and permit lateral passage of fluid when in the second configuration by aligned ports in the tool or sleeve and the tubular body.

The apparatus may comprise a collet. The seat may be formed on, or by, the collet.

The object engaging surface may be formed on, or coupled to, the collet. For example, the collet may comprise a plurality of collet fingers and the object engaging surface may be formed on, or coupled to, at least one, and in particular embodiments all, of the collet fingers.

The collet may be formed on, or coupled to, the tubular body. In particular embodiments, however, the collet may be formed on, or coupled to, the bore member sleeve. In use, the collet may be configured to catch the object in order to permit a borehole operation to be carried out and configured to release the object.

The object may comprise a seat engaging surface. The seat engaging surface may be of any suitable form and construction. The seat engaging surface may be configured to minimise the contact area between the seat and the object; in contrast to conventional arrangements which seek to maximise the contact area between the seat and the object. The seat engaging surface may be configured to provide a line or point engagement between the seat and the object. The seat engaging surface may comprise a curved convex surface portion. The seat engaging surface may comprise a hemi-toroidal surface, d-shaped in longitudinal section or the like. The seat engaging surface may comprise a linear convex surface. For example, the seat engaging surface may comprise a toroidal polyhedron surface, triangular in longitudinal section or the like.

A connector may be provided for coupling the apparatus to an uphole component of the tubular string. In particular embodiments, the connector may comprise a threaded pin connector. In other embodiments, the connector may comprise a threaded box connector, quick connect arrangement or any other suitable connector or combination of these.

A connector may be provided for coupling the apparatus to a downhole component of the tubular string. In particular embodiments, the connector may comprise a threaded box connector. In other embodiments, the connector may comprise a threaded pin connector, quick connect arrangement or any other suitable connector or combination of these.

The apparatus may be operatively associated with a downhole tool.

In use, the apparatus may be configured to move the downhole tool from a first configuration to a second configuration. The first configuration may comprise a run-in configuration. The second configuration may comprise an activated configuration.

The downhole tool operatively associated with the apparatus may be provided upstream of the seat. In such embodiments, the apparatus may be configured to pull the downhole tool to move the downhole tool from the first configuration to the second configuration.

The downhole tool operatively associated with the apparatus may be provided downstream of the seat. In such embodiments, the apparatus may be configured to push the downhole tool to move the downhole tool from the first configuration to the second configuration.

The apparatus may be operatively associated with a single downhole tool. Alternatively, the apparatus may be operatively associated with a plurality of downhole tools.

The downhole tool operatively associated with the apparatus may be of any suitable form and construction.

In particular embodiments, the downhole tool may comprise a sleeve.

The downhole tool may comprise a lateral fluid flow passage, for example but not exclusively a port. The lateral fluid flow passage may comprise at least one fluid port. The lateral fluid flow passage may comprise a single port. Alternatively, the lateral fluid flow passage may comprise a plurality of ports. In embodiments where a plurality of lateral fluid flow ports, two or more of the ports may be arranged circumferentially. Alternatively, or additionally, two or more of the ports may be arranged axially.

At least one downhole tool may comprise a seat.

Where a plurality of downhole tools are provided, at least two of the downhole tools may comprise a seat. In particular embodiments, the seats of at least two of the downhole tools may be configured to receive an object of the same size. Alternatively or in addition, the seat of at least one of the downhole tools may be configured to receive an object of different size to that received in another seat.

At least one downhole tool may comprise a collet and the seat may be formed by the collet.

The object engaging surface may be formed on, or coupled to, the collet. For example, the collet may comprise a plurality of collet fingers and the object engaging surface may be formed on, or coupled to, at least one, and in particular embodiments all, of the collet fingers. In use, the collet may be configured to catch the object in order to permit a borehole operation to be carried out and configured to release the object.

According to a second aspect of the present invention there is provided a method of constructing a downhole apparatus comprising:

providing a seat configured to receive an object; and

providing a convex object engaging surface on the seat.

A tubular body or housing may be provided, the tubular body configured to permit passage of an object.

In particular embodiments, providing the convex object engaging surface may comprise forming the convex object engaging surface on the seat. Any suitable means for forming the convex object engaging surface may be used. For example, the convex object engaging surface may be formed by machining, grinding or combinations of these.

According to a third aspect of the present invention there is provided a method of activating a downhole tool comprising:

providing a downhole apparatus according to the first aspect;

engaging an object with the seat, the engagement between the object and the seat permitting an applied fluid pressure or applied fluid pressure differential to activate a downhole tool.

According to a fourth aspect of the present invention there is provided a seat configured to receive an object, the seat comprising a convex object engaging surface.

An object, such as the object described above with respect to any previous aspect, may be provided in combination with the seat.

It should be understood that the features defined above in accordance with any aspect of the present invention or below in relation to any specific embodiment of the invention may be utilised, either alone or in combination with any other defined feature, in any other aspect or embodiment or to form a further aspect or embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1A is a longitudinal section view of an apparatus according to a first embodiment of the present invention;

FIG. 1B is a longitudinal section view of the apparatus of FIG. 1A, showing an object engaged with a seat;

FIG. 10 is a cross sectional view A-A of the apparatus of 1B, showing the object engaged with the seat;

FIGS. 1D and 1E are longitudinal section views of the apparatus of FIGS. 1A to 10, showing the use of applied pressure to actuate a downhole tool operatively associated with the apparatus; FIG. 2A is a longitudinal section view of an apparatus according to a second embodiment of the present invention, the apparatus shown in a first position;

FIG. 2B is a longitudinal section view of the apparatus of FIG. 2A, showing an object engaged with a seat;

FIG. 2C is a longitudinal section view of the apparatus of FIGS. 2A and 2B, shown in a second position;

FIG. 3A is a longitudinal section view of an apparatus according to a third embodiment of the present invention, the apparatus shown in a first position;

FIG. 3B is a longitudinal section view of the apparatus of FIG. 3A, showing an object engaged with a seat;

FIG. 3C is a longitudinal section view of the apparatus of FIGS. 3A and 3B, the apparatus shown in a second position;

FIG. 4A is a longitudinal section view of an apparatus according to a fourth embodiment of the present invention, the apparatus shown in a first position;

FIG. 4B is a longitudinal section view of the apparatus of FIG. 4A, showing an object engaged with a seat;

FIG. 4C is a longitudinal section view of the apparatus of FIGS. 4A and 4B, the apparatus shown in a second position;

FIG. 5A is a longitudinal section view of an apparatus according to a fifth embodiment of the present invention, the apparatus shown in a first position;

FIG. 5B is a longitudinal section view of the apparatus of FIG. 5A, showing an object engaged with a seat;

FIG. 5C is a longitudinal section view of the apparatus of FIGS. 5A and 5B, the apparatus shown in a second position;

FIG. 6A is a longitudinal section view of an apparatus according to a sixth embodiment of the present invention, the apparatus shown in a first position;

FIG. 6B is a longitudinal section view of the apparatus of FIG. 6A, showing an object engaged with a seat;

FIG. 6C is a longitudinal section view of the apparatus of FIGS. 6A and 6B, the apparatus shown in a second position;

FIG. 7A is a longitudinal section view of an apparatus according to a seventh embodiment of the present invention, the apparatus shown in a first position;

FIG. 7B is a longitudinal section view of the apparatus of FIG. 7A, showing an object engaged with a seat;

FIG. 7C is a longitudinal section view of the apparatus of FIGS. 7A and 7B, the apparatus shown in a second position;

FIG. 8A is a longitudinal section view of an apparatus according to a eighth embodiment of the present invention, the apparatus shown in a first position;

FIG. 8B is a longitudinal section view of the apparatus of FIG. 8A, showing an object engaged with a seat;

FIG. 8C is a longitudinal section view of the apparatus of FIGS. 8A and 8B, the apparatus shown in a second position;

FIG. 9A is a longitudinal section view of an apparatus according to a ninth embodiment of the present invention, the apparatus shown in a first position;

FIG. 9B is a longitudinal section view of the apparatus of FIG. 9A, showing an object engaged with a seat;

FIG. 9C is a longitudinal section view of the apparatus of FIGS. 9A and 9B, the apparatus shown in a second position;

FIG. 9D is a longitudinal section view of the apparatus of FIGS. 9A, 9B and 9C, the apparatus shown in a third position;

FIG. 10A is a longitudinal section view of an apparatus according to a tenth embodiment of the present invention, the apparatus shown in a first position;

FIG. 10B is a longitudinal section view of the apparatus of FIG. 10A, showing an object engaged with a seat;

FIG. 10C is a longitudinal section view of the apparatus of FIGS. 10A and 10B, the apparatus shown in a second position;

FIG. 10D is a longitudinal section view of the apparatus of FIGS. 10A, 10B and 100, the apparatus shown in a third position;

FIG. 11 is an enlarged view of a portion of an apparatus according to an embodiment of the present invention, showing transfer of forces; and

FIG. 12 is a cross section view A-A of the apparatus of FIG. 1B showing a segmented seat according to an alternative embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring first to FIG. 1A to 1E, there is shown an apparatus 10 according to a first embodiment of the present invention. As shown, the apparatus 10 forms part of a tubular string S, such as a completion string, running string, drilling string or the like, the string S being suitable for location in a borehole, such as an oil or gas well borehole B. The section of the string S shown includes the apparatus 10, two tubular string sections S1, S2 and a downhole tool T and, in use, the apparatus 10 is used to activate the downhole tool T as will be described below. In the illustrated embodiment, the downhole tool T is provided with a lateral fluid flow passage in the form of one or more lateral port LP (one port LP is shown) and a plug in the form of one or more rupture disc RD is sealingly disposed in the/each lateral port LP. However, it will understood that the tool T may comprise any suitable downhole tool and may, for example, comprise a valve, a sleeve, a fracking tool, an in-flow control device or other pressure actuable tool.

Referring now in particular to FIGS. 1A and 1B, the apparatus 10 has a tubular body 12 having an axial throughbore 14 configured to permit passage of an object, such as a ball 16 (shown in FIG. 1B). A seat 18 is provided for receiving the ball 16, the seat 18 having a first, uphole-directed, surface 20 and a second, downhole-directed, surface 22. As shown in FIGS. 1A and 1B, the first surface 20 comprises or defines a convex object engaging surface 24 for engaging the ball 16. In the illustrated embodiment, the whole of the first surface 20 is convex, however it will be understood that in other embodiments only part of the first surface 20 may be convex. Also, in the illustrated embodiment, the first surface 20 and the second surface 22 are integrally formed with the tubular body 12 and an intermediate section 26 is formed between the first surface 20 and the second surface 22. However, it will be understood that the seat 18 may comprise only the first surface 20 or the second surface 22 and may be provided without an intermediate section 24. The seat 18 may also comprise a separate component coupled, mounted or otherwise disposed within the throughbore 14 of the tubular body 12.

Referring also to FIGS. 1D and 1E, the seat 18 defines a reduced diameter portion relative to the throughbore 14 and, in use, the ball 16 is dropped, pumped or otherwise motivated through the string S and the throughbore 14 until the ball 16 lands on the seat 18. FIGS. 1B to 1E show the apparatus 10 of FIG. 1A, with the ball 16 engaged in the seat 18.

In this first embodiment, the apparatus 10 is configured so that the engagement between the ball 16 and the seat 18 seals or at least restricts fluid passage downstream of the seat 18 to increase upstream fluid pressure P, the increased upstream fluid pressure P being used to perform or permit a borehole operation to be carried out by activating the tool T. By way of example, the increased upstream pressure may exceed a threshold value required to burst the rupture disk(s) RD in the tool T to permit fluid communication between the throughbore 14 and annulus A disposed between the apparatus 10 and the wall W of the borehole B.

In use, the convex object engaging surface 24 provides an opposing, rather than complementary or matching, engaging surface for landing the ball 16 and provides a reduced or minimal contact surface, preferably a line or point contact, between the ball 16 and the seat 18, thereby preventing or at least mitigating the possibility of the ball 16 becoming swaged or otherwise lodged in the seat 18. By preventing or at least mitigating the possibility of swaging, jamming or otherwise lodging of the ball 16 in the seat 18, the obstruction created by engagement of the ball 16 with the seat 18 may be removed where required. In the illustrated embodiment, removal of the ball 16 may be achieved by reverse circulation (from bottom to top as shown in the figures) or by increasing pressure P to a level capable of extruding the ball 16 through the seat 18.

It will be recognised that the seat 18 according to the present invention may be used in a variety of apparatus or downhole tools and a number of alternative embodiments of the invention will now be described with reference to FIGS. 2A to 12. For ease of reference, the other components of the string S have been removed.

Referring now to FIGS. 2A, 2B and 2C, there is shown an apparatus 210 according to a second embodiment of the invention, like components between the apparatus 210 and those of the first embodiment being represented by like numerals preceded by 2. FIG. 2A shows a longitudinal section view of the apparatus 210 in a first position. FIG. 2B shows a longitudinal section view of the apparatus 210, with a ball 216 engaged in a seat 218. FIG. 2C shows a longitudinal section view of the apparatus 210 in a second position.

As can be seen from FIGS. 2A to 2C, the seat 218 is disposed on a sleeve 28 slidably mounted in an axial throughbore 214 of tubular body 212. The sleeve 28 is retained in the position shown in FIG. 2A by one or more retainer, for example but not exclusively a shear pin 30 or the like. In this embodiment, tubular body 212 further comprises a lateral flow passage, in the form of a lateral port 32, and in the first position shown in FIG. 2A fluid flow through the lateral port 32 is prevented by the sleeve 28. Fluid leakage between the sleeve 28 and the tubular body 212 is prevented by seal elements 34 a, 34 b disposed in recesses 36 a, 36 b provided in the tubular body 212. One or more seal element (not shown) and one or more recess (not shown) may also be provided in the sleeve 28.

In use, the ball 216 (shown in FIGS. 2B and 2C) is dropped, pumped or otherwise motivated through the string S and into the bore 214 of the tubular body 212 until it lands on the seat 218, as shown in FIG. 2B. In this second embodiment, the apparatus 210 is configured so that engagement between the ball 216 and the seat 218 seals or at least restricts fluid passage through the tubular body 212 to provide a fluid pressure differential PD across the seat 218, the fluid pressure differential PD being utilised to perform or permit a borehole operation to be carried out, in this embodiment shear the shear pin 30 and move the sleeve 28 relative to the tubular body 212 from the position shown in FIG. 2A to the position shown in FIG. 2C, in which position access to the lateral port 32 is provided to permit fluid between the throughbore 214 and the annulus A.

As in the first embodiment, in use, convex object engaging surface 224, provides an opposing, rather than complementary, engaging surface for landing the ball 216 and provides a reduced or minimal contact surface, preferably a line or point contact, between the ball 216 and the seat 218, thereby preventing or at least mitigating the possibility of the ball 216 becoming swaged or otherwise lodged in the seat 218. By preventing or at least mitigating the possibility of swaging, jamming or otherwise lodging of the ball 216 in the seat 218, the obstruction created by engagement of the ball 216 with the seat 218 may be removed where required. In the illustrated embodiment, removal of the ball 216 may be achieved by reverse circulation (from bottom to top as shown in the figures) or by increasing the pressure differential PD to a level capable of extruding the ball 216 through the seat 218.

Referring now to FIGS. 3A, 3B and 3C, there is shown an apparatus 310 according to a third embodiment of the invention, like components between the apparatus 310 and those described in previous embodiments being represented by like numerals preceded by 3. FIG. 3A shows a longitudinal section view of the apparatus 310 in a first position. FIG. 3B shows a longitudinal section view of the apparatus 310, with a ball 316 engaged in a seat 318. FIG. 3C shows a longitudinal section view of the apparatus 310 in a second position.

The apparatus 310 is similar to the apparatus 210, the difference being that the sleeve 328 in this third embodiment also comprises a lateral flow passage, in the form of one or more lateral port 38 (one port 38 is shown).

In use, the ball 316 is dropped, pumped or otherwise motivated through the string S and into throughbore 314 of tubular body 312 until it lands on the seat 318. In this third embodiment, the apparatus 310 is configured so that engagement between the ball 316 and the seat 318 seals or at least restricts fluid passage through the tubular body 312 to provide a fluid pressure differential PD across the seat 318, the fluid pressure differential PD being utilised to perform or permit a borehole operation to be carried out, in this embodiment shear the shear pin 330 and move the sleeve 328 relative to the tubular body 312 from the position shown in FIG. 3A to the position shown in FIG. 3C, in which position the lateral port 38 of sleeve 328 is aligned with the lateral port 332 of tubular body 312 to permit fluid between the throughbore 314 and the annulus A. As in the previous embodiment, fluid leakage between the sleeve 328 and the tubular body 312 is prevented by seal elements 334 a, 334 b disposed in recesses 336 a, 336 b provided in the tubular body 312. One or more seal element (not shown) and one or more recess (not shown) may also be provided in the sleeve 328. As in previous embodiments, in use, convex object engaging surface 324, provides an opposing, rather than complementary, engaging surface for landing the ball 316 and provides a reduced or minimal contact surface, preferably a line or point contact, between the ball 316 and the seat 318, thereby preventing or at least mitigating the possibility of the ball 316 becoming swaged or otherwise lodged in the seat 318. By preventing or at least mitigating the possibility of swaging, jamming or otherwise lodging of the ball 316 in the seat 318, the obstruction created by engagement of the ball 316 with the seat 318 may be removed where required. In the illustrated embodiment, removal of the ball 316 may be achieved by reverse circulation (from bottom to top as shown in the figures) or by increasing the pressure differential PD to a level capable of extruding the ball 316 through the seat 318.

Referring now to FIGS. 4A, 4B and 4C, there is shown an apparatus 410 according to a fourth embodiment of the invention, in this embodiment like components between the apparatus 410 and those described in previous embodiments being represented by like numerals preceded by 4. FIG. 4A shows a longitudinal section view of the apparatus 410 in a first position. FIG. 4B shows a longitudinal section view of the apparatus 410, with a ball 416 engaged in a seat 418. FIG. 4C shows a longitudinal section view of the apparatus 410 in a second position.

The apparatus 410 is similar to the second embodiment shown in FIGS. 2A to 2C, the difference being that apparatus sleeve 428 is coupled to a downhole tool T. In the illustrated embodiment, the downhole tool T comprises a sleeve 40. The downhole tool T is disposed downstream or downhole of the seat 418 and, in use, the ball 416 is dropped, pumped or otherwise motivated through the string S and into the bore 414 of the tubular body 412 until it lands on the seat 418, as shown in FIG. 4B. In this fourth embodiment, the apparatus 410 is configured so that engagement between the ball 416 and the seat 418 seals or at least restricts fluid passage through the tubular body 412 to provide a fluid pressure differential PD across the seat 418, the fluid pressure differential PD being utilised to perform or permit a borehole operation to be carried out, in this embodiment shear the shear pin 430 and move the sleeve 428 and sleeve 40 relative to the tubular body 412 from the position shown in FIG. 4A to the position shown in FIG. 4C, in which position access to the lateral port 432 in tubular body 412 is provided, permitting fluid between the throughbore 414 and the annulus A. In this embodiment, the fluid pressure differential PD is used to push the sleeve 428, tool T, sleeve 40 from the first position shown in FIGS. 4A and 4B to the second position shown in FIG. 4C. As in previous embodiments, fluid leakage between the sleeve 428 and the tubular body 412 is prevented by seal elements 434 a, 434 b disposed in recesses 436 a, 436 b provided in the tubular body 412. One or more seal element (not shown) and one or more recess (not shown) may also be provided in the sleeve 428.

As in previous embodiments, in use, convex object engaging surface 424, provides an opposing, rather than complementary, engaging surface for landing the ball 416 and provides a reduced or minimal contact surface, preferably a line or point contact, between the ball 416 and the seat 418, thereby preventing or at least mitigating the possibility of the ball 416 becoming swaged or otherwise lodged in the seat 418. By preventing or at least mitigating the possibility of swaging, jamming or otherwise lodging of the ball 416 in the seat 418, the obstruction created by engagement of the ball 416 with the seat 418 may be removed where required. In the illustrated embodiment, removal of the ball 416 may be achieved by reverse circulation (from bottom to top as shown in the figures) or by increasing the pressure differential PD to a level capable of extruding the ball 416 through the seat 418.

Referring now to FIGS. 5A, 5B and 5C, there is shown an apparatus 510 according to a fifth embodiment of the invention, like components between the apparatus 510 and those of previous embodiments being represented by like numerals preceded by 5. FIG. 5A shows a longitudinal section view of the apparatus 510 in a first position. FIG. 5B shows a longitudinal section view of the apparatus 510, with a ball 516 engaged in a seat 518. FIG. 5C shows a longitudinal section view of the apparatus 510 in a second position.

The apparatus 510 is similar to the apparatus 410 shown in FIGS. 4A to 4C, the difference being that the sleeve 528 also comprises a lateral flow passage, in the form of a lateral port 538.

In use, the ball 516 is dropped, pumped or otherwise motivated through the string S and into throughbore 514 of tubular body 512 until it lands on the seat 518. In this fifth embodiment, the apparatus 510 is configured so that engagement between the ball 516 and the seat 518 seals or at least restricts fluid passage through the tubular body 512 to provide a fluid pressure differential PD across the seat 518, the fluid pressure differential PD being utilised to perform or permit a borehole operation to be carried out, in this embodiment shear the shear pin 530 and move the apparatus sleeve 528 and tool sleeve 540 relative to the tubular body 512 from the position shown in FIGS. 5A and 5B to the position shown in FIG. 5C, in which position the lateral port 538 of sleeve 528 is aligned with the lateral port 532 of tubular body 512 to permit fluid between the throughbore 514 and the annulus A. As in previous embodiments, fluid leakage between the sleeve 528 and the tubular body 512 is prevented by seal elements 534 a, 534 b disposed in recesses 536 a, 536 b provided in the tubular body 512. One or more seal element (not shown) and one or more recess (not shown) may also be provided in the sleeve 528 or tool sleeve 540.

As in previous embodiments, in use, convex object engaging surface 524, provides an opposing, rather than complementary, engaging surface for landing the ball 516 and provides a reduced or minimal contact surface, preferably a line or point contact, between the ball 516 and the seat 518, thereby preventing or at least mitigating the possibility of the ball 516 becoming swaged or otherwise lodged in the seat 518. By preventing or at least mitigating the possibility of swaging, jamming or otherwise lodging of the ball 516 in the seat 518, the obstruction created by engagement of the ball 516 with the seat 518 may be removed where required. In the illustrated embodiment, removal of the ball 516 may be achieved by reverse circulation (from bottom to top as shown in the figures) or by increasing the pressure differential PD to a level capable of extruding the ball 516 through the seat 518.

Referring now to FIGS. 6A, 6B and 6C, there is shown an apparatus 610 according to a sixth embodiment of the invention, like components between the apparatus 610 and those of previous embodiments being represented by like numerals preceded by 6. FIG. 6A shows a longitudinal section view of the apparatus 610 in a first position. FIG. 6B shows a longitudinal section view of the apparatus 610, with a ball 616 engaged in a seat 618. FIG. 6C shows a longitudinal section view of the apparatus 610 in a second position.

The apparatus 610 is similar to the apparatus 410 shown in FIGS. 4A to 4C, the difference being that the apparatus 610 is coupled to a downhole tool T disposed upstream or uphole of the seat 618 and, in use, the ball 616 is dropped, pumped or otherwise motivated through the string S and into the throughbore 614 of the tubular body 612 until it lands on the seat 618, as shown in FIG. 6B. In this sixth embodiment, the apparatus 610 is configured so that engagement between the ball 616 and the seat 618 seals or at least restricts fluid passage through the tubular body 612 to provide a fluid pressure differential PD across the seat 618, the fluid pressure differential PD being utilised to perform or permit a borehole operation to be carried out, in this embodiment shear the shear pin 630 and move the apparatus sleeve 628 and tool sleeve 640 relative to the tubular body 612 from the position shown in FIGS. 6A and 6B to the position shown in FIG. 6C, in which position access to the lateral port 632 in tubular body 612 is provided to permit fluid between the throughbore 614 and the annulus A. In this embodiment, the differential fluid pressure PD is used to push the tool T from the first position shown in FIGS. 6A and 6B to the second position shown in FIG. 6C. As in previous embodiments, fluid leakage between the sleeve 628 and the tubular body 612 is prevented by seal elements 634 a, 634 b disposed in recesses 636 a, 636 b provided in the tubular body 612. One or more seal element (not shown) and one or more recess (not shown) may also be provided in the sleeve 628 or sleeve 640.

As in previous embodiments, in use, convex object engaging surface 624, provides an opposing, rather than complementary, engaging surface for landing the ball 616 and provides a reduced or minimal contact surface, preferably a line or point contact, between the ball 616 and the seat 618, thereby preventing or at least mitigating the possibility of the ball 616 becoming swaged or otherwise lodged in the seat 618. By preventing or at least mitigating the possibility of swaging, jamming or otherwise lodging of the ball 616 in the seat 618, the obstruction created by engagement of the ball 616 with the seat 618 may be removed where required. In the illustrated embodiment, removal of the ball 616 may be achieved by reverse circulation (from bottom to top as shown in the figures) or by increasing the pressure differential PD to a level capable of extruding the ball 616 through the seat 618.

Referring now to FIGS. 7A, 7B and 7C, there is shown an apparatus 710 according to a seventh embodiment of the invention, like components between the apparatus 710 and those of previous embodiments being represented by like numerals preceded by 7. FIG. 7A shows a longitudinal section view of the apparatus 710 in a first position. FIG. 7B shows a longitudinal section view of the apparatus 710, with a ball 716 engaged in a seat 718. FIG. 7C shows a longitudinal section view of the apparatus 710 in a second position.

The apparatus 710 is similar to the apparatus 610 shown in FIGS. 6A to 6C, the difference being that the sleeve 42 also comprises a lateral flow passage, in the form of a lateral port 738. In use, the ball 716 is dropped, pumped or otherwise motivated through the string S and into the throughbore 714 of the tubular body 712 until it lands on the seat 718, as shown in FIG. 7B. In this sixth embodiment, the apparatus 710 is configured so that engagement between the ball 716 and the seat 718 seals or at least restricts fluid passage through the tubular body 712 to provide a fluid pressure differential PD across the seat 718, the fluid pressure differential PD being utilised to perform or permit a borehole operation to be carried out, in this embodiment shear the shear pin 730 and move the apparatus sleeve 728 and tool sleeve 740 relative to the tubular body 712 from the position shown in FIGS. 7A and 7B to the position shown in FIG. 7C, in which position the lateral port 42 of sleeve 740 is aligned with the lateral port 732 of tubular body 712 to permit fluid between the throughbore 714 and the annulus A. In this embodiment, the differential fluid pressure PD is used to pull the tool T, sleeve 740 from the first position shown in FIGS. 7A and 7B to the second position shown in FIG. 7C. Fluid leakage between the sleeve 740 and the tubular body 712 is prevented by seal elements 734 a, 734 b disposed in recesses 736 a, 736 b provided in the tubular body 712. One or more seal element (not shown) and one or more recess (not shown) may also be provided in the sleeve 728. As in previous embodiments, in use, convex object engaging surface 724, provides an opposing, rather than complementary, engaging surface for landing the ball 716 and provides a reduced or minimal contact surface, preferably a line or point contact, between the ball 716 and the seat 718, thereby preventing or at least mitigating the possibility of the ball 716 becoming swaged or otherwise lodged in the seat 718. By preventing or at least mitigating the possibility of swaging, jamming or otherwise lodging of the ball 716 in the seat 718, the obstruction created by engagement of the ball 716 with the seat 718 may be removed where required. In the illustrated embodiment, removal of the ball 716 may be achieved by reverse circulation (from bottom to top as shown in the figures) or by increasing the pressure differential PD to a level capable of extruding the ball 716 through the seat 718.

In any or all of the above embodiments, in addition to eliminating or mitigating the possibility of swaging the ball in the seat, the apparatus may also permit a greater degree of control over the transmission of load forces between the ball and the seat, when engaged, and to other components of, or operatively associated with, the apparatus, for example but not exclusively, downhole tool, tubular body or the surrounding borehole. The engagement between the seat and the ball is configured so that the load path of a resultant force transmitted to the seat may be controlled or selected to increase or maximise the transmission of load forces along a particular vector in order to activate another component of, or operatively associated with, the apparatus and/or to eliminate or mitigate moment forces. Control over the transmission of load forces may additionally or alternatively permit optimisation of parts of the apparatus, or of components operatively associated with the apparatus, since redundancy otherwise required due to the lack of control over the transmission of load forces may be reduced or eliminated.

Referring now to FIGS. 8A, 8B and 8C, there is shown an apparatus 810 according to an eighth embodiment of the invention, like components between the apparatus 810 and previous embodiments being represented by like numerals preceded by 8. FIG. 8A shows a longitudinal section view of the apparatus 810 in a first position. FIG. 8B shows a longitudinal section view of the apparatus 810, with a ball 816 engaged in a seat 818. FIG. 8C shows a longitudinal section view of the apparatus 810 in a second position.

The apparatus 810 is similar to the apparatus 210 shown in FIGS. 2A to 2C, the difference being that in this embodiment, the sleeve 828 comprises a collet 44 having a plurality of circumferentially spaced collet fingers 46, the seat 818 and convex object engaging surface 824 being formed in the collet fingers 46. In use, the ball 816 is dropped, pumped or otherwise motivated through the string S and into the bore 814 of the tubular body 812 until it lands on the seat 818 formed in the collet fingers 46. In this embodiment, the apparatus 810 is configured so that engagement between the ball 816 and the seat 818 seals or at least restricts fluid passage through the tubular body 812 to provide a fluid pressure differential PD across the seat 818, the fluid pressure differential PD being utilised to perform or permit a borehole operation to be carried out, in this embodiment shear the shear pin 830 and move the sleeve 828 relative to the tubular body 812 from the position shown in FIGS. 8A and 8B to the position shown in FIG. 8C, in which position access to the lateral port 832 is provided to permit fluid between the throughbore 814 and the annulus A. As shown in FIG. 8C, in the second position the collet fingers 46 engage a collet finger receiving recess 48 and so the ball 816 is released.

In addition to eliminating or mitigating the possibility of swaging the ball in the seat, in this embodiment the apparatus also permits a greater degree of control over the transmission of load forces between the ball 816 and the seat 818, when engaged, and to other components of, or operatively associated with, the apparatus 810. The engagement between the seat 818 and the ball 816 is configured so that the load path of a resultant force transmitted to the seat 818 may be controlled or selected to increase or maximise the transmission of load forces along a particular vector in order to activate another component of, or operatively associated with, the apparatus and/or to eliminate or mitigate moment forces. Control over the transmission of load forces may additionally or alternatively permit optimisation of parts of the apparatus 810, or of components operatively associated with the apparatus 810, since redundancy otherwise required due to the lack of control over the transmission of load forces may be reduced or eliminated.

Referring to FIGS. 9A, 9B, 9C and 9D, there is shown an apparatus 910 according to a ninth embodiment of the invention, like components between the apparatus 910 and previously described embodiments being represented by like numerals preceded by 9. FIG. 9A shows a longitudinal section view of the apparatus 910 in a first position. FIG. 9B shows a longitudinal section view of the apparatus 910, with a ball 916 engaged in a seat 918. FIG. 9C shows a longitudinal section view of the apparatus 910 in a second position, with the ball 916 engaged in the seat 918. FIG. 9D shows a longitudinal section view of the apparatus 910 in a third position, where the ball 910 has been released.

The apparatus 910 is similar to the apparatus 810 shown in FIGS. 8A to 8C, the difference being that in addition to permitting selective access to a lateral port 932, movement of the sleeve 928 having the collet 942 pushes a downhole tool T, which may also comprise a sleeve 940. In use, the ball 916 is dropped, pumped or otherwise motivated through the string S and into the throughbore 914 of the tubular body 912 until it lands on the seat 918 formed in the collet fingers 944. In this embodiment, the apparatus 910 is configured so that engagement between the ball 916 and the seat 918 seals or at least restricts fluid passage through the tubular body 912 to provide a fluid pressure differential PD across the seat 918, the fluid pressure differential PD being utilised to perform or permit a borehole operation to be carried out, in this embodiment shear the shear pin 930 to move the sleeve 928, collet 944 relative to the tubular body 912 from the position shown in FIGS. 9A and 9B to the position shown in FIG. 9C. Following movement from the position shown in FIG. 9B to the position shown in FIG. 9C, the fluid pressure differential PD may be reduced, with the result that the apparatus 910 moves from the position shown in FIG. 9C to the position shown in FIG. 9D, in which position the apparatus 910 is retracted in an upstream or uphole direction under the influence of a biasing member, spring or the like (represented by spring force k) so that collet fingers 946 engage a collet finger receiving recess 948 now accessible due to the downstream/downhole movement of the tool sleeve 940 and the ball 916 is released.

As in the previous embodiment, in addition to eliminating or mitigating the possibility of swaging the ball in the seat, in this embodiment the apparatus 910, convex object engaging surface 924 also permits a greater degree of control over the transmission of load forces between the ball 916 and the seat 918, when engaged, and to other components of, or operatively associated with, the apparatus 910. The engagement between the seat 918 and the ball 916 is configured so that the load path of a resultant force Fres transmitted to the seat 918 may be controlled or selected to increase or maximise the transmission of load forces along a particular vector in order to activate another component of, or operatively associated with, the apparatus and/or to eliminate or mitigate moment forces. Control over the transmission of load forces may additionally or alternatively permit optimisation of parts of the apparatus 910, or of components operatively associated with the apparatus 910, since redundancy otherwise required due to the lack of control over the transmission of load forces may be reduced or eliminated.

Referring to FIGS. 10A, 10B, 10C and 10D, there is shown an apparatus 1010 according to a tenth embodiment of the invention, like components between the apparatus 1010 and previously described embodiments being represented by like numerals preceded by 10. FIG. 10A is a longitudinal section view of an apparatus 1010, the apparatus 1010 shown in a first position. FIG. 10B is a longitudinal section view of the apparatus 1010, showing a ball 1016 engaged with a first seat 1018 a. FIG. 10C is a longitudinal section view of the apparatus 1010, the apparatus shown in a second position in which the ball 1016 is engaged with a second seat 1018 b. FIG. 10D is a longitudinal section view of the apparatus 1010, the apparatus 1010 shown in a third position.

In this embodiment, the apparatus 1010 comprises, or forms part of, a downhole tool T, the downhole tool T comprising a mechanical counting device or indexing device which in use may be used as fluid divert apparatus. As shown, tubular body 1012 comprises a plurality of collet finger receiving recesses 1048 a,1048 b,1048 c and 1048 d and in the illustrated embodiment, the apparatus 1010 comprises two sleeves 1028 a, 1028 b, each sleeve 1028 a, 1028 b having a collet 1044 a, 1044 b. It will be recognised that any number of sleeves 1028 may be provided. The downhole tool T further comprises a sleeve 1040.

In use, the ball 1016 is dropped, pumped or otherwise motivated through the string S and into the bore 1014 of the tubular body 1012 until it lands on the seat 1018 formed in the collet fingers 1046 of the first sleeve 1028 a. In the position shown in FIG. 10A, the collet fingers 1046 a of the first sleeve 1028 a define a position capable to catching the ball 1016 while the collet fingers 1046 b of the second sleeve 1028 b are engaged in third collet finger receiving recess 1048 c. The apparatus 1010 is configured so that engagement between the ball 1016 and the seat 1018 of the first sleeve 1028 a seals or at least restricts fluid passage through the tubular body 1012 to provide a fluid pressure differential PD across the seat 1018, the fluid pressure differential PD being utilised to move the sleeves 1028 a, 1028 b, and sleeve 1040 relative to the tubular body 1012 from the position shown in FIG. 10B to the position shown in FIG. 100. In this position, the collet fingers 1046 a of the first sleeve 1028 a engage first collet finger receiving recess 1048 a while the collet fingers 1046 b of the second sleeve 1028 b have translated out of collet receiving recess 1048 c and so define a position capable of catching the ball 1016 as it is released from the first sleeve 1028 a. The apparatus 1010 is configured so that engagement between the ball 1016 and the seat 1018 b of the second sleeve 1028 b seals or at least restricts fluid passage through the tubular body 1012 to provide a fluid pressure differential PD across the seat 1018 b, the fluid pressure differential PD being utilised to move the sleeves 1028 a, 1028 b and sleeve 1040 relative to the tubular body 1012 from the position shown in FIG. 100 to the position shown in FIG. 10D. In this position, the collet fingers 1046 a of the first sleeve 1028 a have translated out of their collet receiving recess 1048 a while the collet fingers 1046 b of the second sleeve 1028 b engage the fourth collet finger receiving recess 1048, in which position the ball 1016 is released.

As in the previous embodiments, in addition to eliminating or mitigating the possibility of swaging the ball in the seat, in this embodiment the apparatus 1010, convex object engaging surfaces 1024 a, 1024 b of seats 1018 a, 1018 b also permit a greater degree of control over the transmission of load forces between the ball 1016 and the seats 1018 a, 1018 b, when engaged, and to other components of, or operatively associated with, the apparatus 1010. The engagement between the seats 1018 a,1018 b and the ball 1016 is configured so that the load path of a resultant force Fres transmitted to the seats 1018 may be controlled or selected to increase or maximise the transmission of load forces along a particular vector in order to activate another component of, or operatively associated with, the apparatus and/or to eliminate or mitigate moment forces. Control over the transmission of load forces may additionally or alternatively permit optimisation of parts of the apparatus 1010, or of components operatively associated with the apparatus 1010, since redundancy otherwise required due to the lack of control over the transmission of load forces may be reduced or eliminated.

Referring now to FIG. 11, as described above, in any or all of the above embodiments, in addition to eliminating or mitigating the possibility of swaging the ball in the seat, the apparatus may also permit a greater degree of control over the transmission of load forces between the ball and the seat, when engaged, and to other components of, or operatively associated with, the apparatus, for example but not exclusively, downhole tool T, tubular body or the surrounding borehole B For example, as shown in FIG. 11—which shows an enlarged view of a portion of an apparatus 1110 according to another embodiment of the present invention, showing transfer of forces—the engagement between the seat 1118, convex surface 1124 and the ball is configured so that the load path of a resultant force (Fres) of radial (Frad) and axial (Fax) forces transmitted to the seat may be controlled or selected to increase or maximise the transmission of load forces along a particular vector in order to activate another component of, or operatively associated with, the apparatus and/or to eliminate or mitigate moment forces. Alternatively or in addition, control over the transmission of load forces may additionally or alternatively permit optimisation of parts of the apparatus, or of components operatively associated with the apparatus, since redundancy otherwise required due to the lack of control over the transmission of load forces may be reduced or eliminated.

It should be understood that the embodiments described herein are merely exemplary and that various modifications may be made thereto without departing from the scope of the invention.

For example, while in the illustrated embodiments, the convex object engaging surface or surfaces are annular and form a continuous surface, in alternative embodiments such as shown illustratively in FIG. 12, the convex object engaging surface for receiving ball 1216 may comprise a number of segments 1224 a,b,c,d or the like.

For example, while in the illustrated embodiment the object comprises a ball, in other embodiments the object may comprise a dart, plug member, or the like.

For example, while in some embodiments the seat or parts thereof are integrally formed with the tubular body, in other embodiments the seat or parts may comprise, or be provided on, a separate component. 

1. A downhole apparatus or tool comprising: a seat configured to receive an object, the seat comprising a convex object engaging surface.
 2. The apparatus of claim 1, comprising a tubular body or housing configured to permit passage of the object.
 3. The apparatus of claim 1, wherein the object comprises a ball.
 4. (canceled)
 5. The apparatus of claim 2, wherein one of: the apparatus is configured so that engagement between the object and the seat seals or at least restricts fluid passage through the tubular body; the apparatus is configured so that engagement between the object and the seat seals or at least restricts fluid passage through the tubular body to increase upstream fluid pressure; the apparatus is configured so that engagement between the object and the seat seals or at least restricts fluid passage through the tubular body to increase upstream fluid pressure to perform or permit a downhole operation. 6-13. (canceled)
 14. The apparatus of claim 1, wherein the apparatus is configured so that engagement between the seat and the object controls or selects the load path of a resultant force transmitted to the seat.
 15. The apparatus of claim 14, wherein the apparatus is configured so that the engagement between the seat and the object controls or selects the load path of a resultant force transmitted to the seat to at least one of: increase or maximise the transmission of load forces along a particular vector, increase or maximise the transmission of load forces along a particular vector to activate another component of, or operatively associated with, the apparatus; eliminate or mitigate moment forces. 16-17. (canceled)
 18. The apparatus of claim 1, wherein the object engaging surface comprises, or forms part of, at least one of: an upstream or uphole directed surface of the seat; and a downstream or downhole directed surface of the seat. 19-22. (canceled)
 23. The apparatus of claim 1, wherein the object engaging surface is configured to provide a line or point engagement between the seat and the object.
 24. The apparatus of claim 1, wherein one of: the object engaging surface comprises a curved convex surface portion; the object engaging surface comprises a hemi-toroidal surface; the object engaging surface is d-shaped in longitudinal section; the object engaging surface comprises a linear convex surface; the object engaging surface comprises a toroidal polyhedron surface; the object engaging surface is triangular in longitudinal section. 25-29. (canceled)
 30. The apparatus of claim 2, wherein the object engaging surface is angled with respect to a longitudinal axis of the body.
 31. (canceled)
 32. The apparatus of claim 1, wherein the object engaging surface is annular.
 33. The apparatus of claim 1, wherein the apparatus is configured to provide a plurality of distinct points of contact with the object.
 34. The apparatus of claim 33, wherein the seat comprises a plurality of circumferentially or radially spaced components or segments. 35-40. (canceled)
 41. The apparatus of claim 2, wherein the tubular body comprises a lateral fluid flow passage.
 42. The apparatus of claim 41, wherein at least one of: the lateral fluid flow passage comprises at least one port; the lateral fluid flow passage comprises a plurality of ports; the lateral fluid flow passage comprises a plurality of ports, two or more of the ports are arranged circumferentially; two or more of the ports are arranged circumferentially, two or more of the ports are arranged axially. 43-48. (canceled)
 49. The apparatus of claim 2, wherein the seat is integrally formed with the tubular body.
 50. The apparatus claim 2, wherein the seat is coupled to the tubular body.
 51. The apparatus of claim 50, wherein the seat is provided, coupled to or formed on a bore member or sleeve operatively associated with the tubular body. 52-54. (canceled)
 55. The apparatus of claim 51, wherein the bore member or sleeve comprises a lateral fluid flow passage.
 56. The apparatus of claim 55, wherein at least one of: the lateral fluid flow passage comprises at least one port; the lateral fluid flow passage comprises a plurality of ports; the lateral fluid flow passage comprises a plurality of ports, two or more of the ports arranged circumferentially; the lateral fluid flow passage comprises a plurality of ports, two or more of the ports arranged axially. 57-59. (canceled)
 60. The apparatus of claim 1, wherein the apparatus comprises a collet.
 61. The apparatus of claim 60, wherein the seat is formed on, or by, the collet.
 62. The apparatus of claim 60, wherein the object engaging surface is formed on, or coupled to, the collet.
 63. The apparatus of claim 60, wherein the collet comprises a plurality of collet fingers and the object engaging surface is formed on, or coupled to, at least one of the collet fingers.
 64. The apparatus of claim 2, wherein the collet is formed on, or coupled to, the tubular body.
 65. The apparatus of claim 51, wherein the collet is formed on, or coupled to, the bore member or sleeve.
 66. The apparatus of claim 60, wherein at least one of: the collet is configured to catch the object to permit a borehole operation to be carried out; the collet is configured to release the object. 67-68. (canceled)
 69. The apparatus of claim 1, in combination with the object. 70-74. (canceled)
 75. The apparatus of claim 1, wherein the apparatus is operatively associated with at least one downhole tool.
 76. The apparatus of claim 75, wherein at least one of: the downhole tool comprises a sleeve; the apparatus is configured to pull or push the downhole tool to move the downhole tool from a first configuration to a second configuration. 77-78. (canceled)
 79. The apparatus of claim 75, wherein the downhole tool comprises a lateral fluid flow passage.
 80. The apparatus of claim 79, wherein at least one of: the lateral fluid flow passage comprises at least one fluid port; the lateral fluid flow passage comprises a plurality of ports; the lateral fluid flow passage comprises a plurality of ports, two or more of the ports arranged circumferentially; the lateral fluid flow passage comprises a plurality of ports, two or more of the ports arranged axially. 81-89. (canceled)
 90. A method of constructing a downhole apparatus comprising: providing a seat configured to receive an object; and providing a convex object engaging surface on the seat.
 91. A method of activating a downhole tool comprising: providing a downhole apparatus according to claim 1; engaging an object with the object engaging surface of the seat of said downhole apparatus, the engagement between the object and the seat permitting an applied fluid pressure or applied fluid pressure differential to activate the downhole tool.
 92. (canceled)
 93. Use of a downhole apparatus according to claim 1 to prevent swaging, jamming or lodging of an object in a seat.
 94. The apparatus of claim 1, wherein the seat comprises a plurality of circumferentially or radial components or segments, and wherein the convex object engaging surface is formed on, or coupled to, said components or segments. 